1. Field of the Invention
The present invention relates to a crystal oscillator for measuring crystal impedance (CI) of a crystal unit.
2. Description of the Related Art
The resistance substitution method is conventionally known as a method of measuring crystal impedance (CI) of a crystal unit.
In the resistance substitution method, a crystal unit to be measured is incorporated into a feedback loop of a self-oscillator, and an impedance upon completely serially exciting the crystal unit to be measured is measured as representing CI of the crystal unit.
In the resistance substitution method, however, it is necessary to measure CI under a pure serial resonance frequency. Oscillation is therefore at a frequency different from the actual oscillation frequency. Another problem is that adjustment and setting of an oscillation frequency and setting of a driving power of the crystal unit take a long period of time. When measuring CI of a crystal unit for diverse and various oscillation frequencies, there are required very complicated operations such as switching of frequency ranges and setting of an oscillation level.